The coronaviruses are a large group of viruses including hundreds of individual species. A wide range of hosts, including humans, mice, cows, pigs, dogs, turkeys, and cats are susceptible to coronavirus infection.
There are 10-20 different coronaviruses capable of infecting cats. Among the feline coronaviruses are Feline Infectious Peritonitis Virus (FIPV) and Feline Enteric Coronavirus (FECV). Currently, there is considerable academic debate over whether FIPV and FECV are two distinct species of coronavirus, or whether they are merely strain variations within the same coronavirus species.
Under one theory, FIPV and FECV are distinct species which are responsible for different disease states. According to this theory, FIPV infection may be manifested through either of two types of pathologies. The first form, called the wet or effusive form, results from a massive immune response against the infecting coronavirus during which ascites fluid appears in the animal's coelomic cavity. The effusive form of the disease progresses rapidly and is inevitably fatal.
The second form of the disease, called the dry form, is the consequence of a more effective response of the immune system to the presence of coronavirus infected cells. There is, at first, a localized inflammation with a subsequent "walling off" of the infected cells. This effect generates a nodule, which may occur in various parts of the body. The dry form of the disease may or may not be fatal depending on the localization of the nodule. For example, nodulation within the brain may prove rapidly fatal, whereas nodulation within muscle or the peritoneal wall may be tolerated for prolonged periods.
Regardless of whether the infected cat exhibits the effusive pathology or the dry pathology, once infected, a cat remains infected and is a carrier of the virus for the remainder of its life. The infected cat can transmit the virus to other cats with which it comes in contact. Thus, it is desirable to detect cats capable of transmitting the potentially lethal virus in order to prevent the spread of the disease.
According to the theory holding that FIPV and FECV are distinct species, FECV is responsible for a mild intestinal disorder. FECV infection may or may not result in diarrhea, but is self limiting in either case. Thus, cats infected with FECV completely recover from the infection.
Under the second theory, FIPV and FECV are strain variants within the same species and the pathology exhibited by the infected cat, whether the wet form, the dry form, or enteric disease, is determined by host factors.
Cats exposed to any coronavirus capable of infecting them produce antibodies against generic epitopes common to these coronaviruses. A currently available diagnostic quantitates the levels of antibodies directed against these generic epitopes. Such assays risk misdiagnosis because exposure to any coronavirus can generate an immune response in the cat and thereby yield a positive result in the assay.
Thus a need exists for an assay capable of discriminating between potentially fatal coronaviruses and those which do not pose a significant threat.
Another currently available assay utilizes PCR to detect infection with FIPV. However, in some cases, FIPV infected cats may not yield a positive result in the PCR assay due to the sequestration of the virus in limited regions of the host's body or to differences between the sequences of the primers used in the PCR analysis and the sequence of the viral DNA. Consequently, a need exists for diagnostics which have even greater sensitivity than the PCR based methods. In addition, a need exists for improved PCR based diagnostics which provide increased detection levels relative to those currently available.